The invention relates to a fixation system for bones with a force support having holes and bone screws which are insertable into the holes.
If fragments of broken bones have to be joined to each other plate, nail and fixateur systems are available nowadays. Stability in plate and nail systems has been reached hitherto by the fact that if osteosynthetic plates were used bone screws firmly pulled these plates up to the bones in order to achieve a stabilization of the fragments of broken bones by means of the contact pressure which the plate exerts on the bones. If a marrow nail is used which is in the marrow space stability will also be increased by transversely inserting screws through the bone and the marrow nail. Although these screws are located in the bone by a thread minor motions are possible because the screw passes through the nail.
Different technical solutions were successful in fixedly joining the head of the screw to the plate or to establish a fixed connection between the screw and the marrow nail itself. In this respect, reference is made to EP 0 201 024 B1, DE 43 43 117 A1, DE 196 29 011 A1, and the German Patent Application P 198 58 889.5.
Hence, it is proper to speak of inner fixateur systems in this new generation of implants because the main feature of the outer fixateurs is angular stability between the screw and the transverse force support.
In clinical applications, these fixateur systems have distinctly exhibited a superiority over conventional plate and nail systems up to now.
Holes are oriented perpendicularly to the force support in known fixation systems.
However, if the patient loads the implant with too much of his body weight too early, which is contrary to a doctor's advice, the implant might be spoiled by bending or the implant might break.
It has been observed that if bones are soft and/or are subjected to high loads, particularly by bending, the screws might be torn out of the bone.
FR-A-742 618 discloses obliquely oriented holes in connecting pieces for osteosynthesis. The holes have threads the thread axis of which exactly coincides with the hole axis. Moreover, the connecting pieces have a thickened material region adjacent to the holes. The consequence is that the bone screws can only be inserted in an exactly coaxial relationship with the hole axis. As a result, only unidirectional stability is achieved and the implant involves expenditure in manufacture.
More implants having obliquely directed holes and unidirectionally insertable bone screws have been known from U.S. Pat. No. 5,306,275, U.S. Pat. No. 5,147,361, and U.S. Pat. No. 558,674.
Accordingly, it is the object of the invention to provide a fixation system for bones which allows to simplify its manufacturing technique and to introduce bone screws in an optimal angular orientation in the bones.